1. Field of the Invention
The present invention relates to surface-mounting-type electronic-circuit units.
2. Description of the Related Art
Surface-mounting-type electronic-circuit units are generally structured such that chip components such as resistors and capacitors, and semiconductor components such as transistors, are soldered to the soldered lands of electrically conductive patterns formed on a board. These circuit components are then typically covered with a shielding cover. End-face electrodes are provided at the side face of the board. The end-face electrodes are soldered to the soldered lands of a motherboard so as to surface-mount the electronic-circuit units on to the motherboard.
Such a board is obtained by dividing a large printed circuit board along a series of lattice-shaped division lines. The division lines are formed by a great number of through holes made in the large printed circuit board, and a plating layer, which serves as the end-face electrodes, is formed on each through hole. The large printed circuit board is then divided along division lines (which pass through the centers of the through holes). The end-face electrodes are formed at a side face of each printed circuit board generated by the division.
The technology for making compact circuit components, such as chip components and semiconductor components, has developed remarkably in recent years. For example, very compact chip resistors and chip capacitors having external dimensions of about 0.6 mm by 0.3 mm have recently become commercially available. When such very compact circuit components are mounted on a printed circuit board in a conventional electronic-circuit unit, as described above, with the distances between components being reduced to a minimum, the electronic-circuit unit can be made compact to some extent. However, there is a limitation for making circuit components more compact. In addition, when a great number of circuit components are mounted on a printed circuit board, short-circuiting of the soldered portions of the circuit components needs to be prevented. Therefore, there is also a limitation for reducing the distances between the components. These limitations prevent the size of the electronic-circuit units from being reduced further. In addition, since the end-face electrodes are formed by through holes, the limited mounting space on the printed circuit board is narrowed by the end-face electrodes. This also prevents the electronic-circuit units from being made more compact.
The present invention has been made in consideration of the above conventional technology. Accordingly, it is an object of the present invention to provide a compact, surface-mounting-type electronic-circuit unit, which overcomes the limitations of the conventional technology.
The foregoing object is achieved in one aspect of the present invention through the provision of an electronic-circuit unit including an alumina board; circuit elements including a capacitor, a resistor, and an inductive device, each formed as thin films on the alumina board; an electrically conductive pattern connected to a circuit element and formed as a thin film on the alumina board; a semiconductor bare chip mounted on the alumina board; and an end-face electrode connected to the electrically conductive pattern and formed on a side face of the alumina board, wherein the semiconductor bare chip is wire-bonded to the electrically conductive pattern.
The end-face electrode connected to the electrically conductive pattern may be formed as a thick film on a side face of the alumina board by the use of a low-temperature baked material.
With the above structure, since the circuit elements (including the capacitor, the resistor, and the inductive device) are formed with high precisely by using a thin-film technology, and the semiconductor bare chip is wire-bonded to form a semiconductor device, the required circuit components can be mounted on the alumina board in a high-density configuration to form a compact surface-mounting-type electronic-circuit unit.
It is preferred that Cu layers be formed on surfaces of the capacitor and the inductive device. This increases Q in a resonant circuit.
Since the end-face electrode is formed as a thick film by using a low-temperature baked material, it has a desired film thickness and is formed efficiently in terms of space. The circuit elements, which are formed as thin films; are prevented from being burned out during the baking process for the formation of the end-face electrode.
It is preferred that an Au plating layer be formed on the end-face electrode, which is formed as a thick film. This prevents Ag in the low-temperature baked material from depositing in solder (namely, prevents a silver-being-eaten phenomenon) when the end-face electrode is soldered to the soldered land of a motherboard.
It is preferred that the end-face electrode be formed as a thick film only at each of the two opposing sides of the alumina board. After a large printed circuit board is divided into strip-shaped pieces having a great number of alumina boards, end-face electrodes can then be formed as thick films on the side faces of the strip-shaped piece prior to dividing the strip-shaped piece into separate boards. This procedure is well suited to mass production.
The foregoing object is achieved in another aspect of the present invention through the provision of an electronic-circuit unit having circuit elements, including a capacitor, a resistor, and an inductive device, formed as thin films on an alumina board having a rectangular, plane shape; a semiconductor bare chip wire-bonded on the alumina board; grounding electrodes formed at the ends of two opposing side faces of the alumina board; and an input electrode and an output electrode formed away from the ends.
Since grounding electrodes are formed at the ends of two opposing side faces of the alumina board, and the input electrode and the output electrode are formed away from the ends, even when various adjustments and inspections are performed during a semi-production condition (namely, in a strip-shaped-piece condition) in which a great number of connected alumina boards are obtained by sub-dividing a large printed circuit board, the grounding electrodes eliminate adverse effects on the circuits of adjacent alumina boards.
It is preferred that a shielding cover be mounted to the alumina board so as to cover the circuit elements and the semiconductor bare chip, and that the shielding cover be soldered to the grounding electrodes. This increases a shielding effect.